“If you can’t beat’em, don’t breed’em” seems to be the theory behind a new toxin-free antifouling developed by a team of Swedish scientists.
The coating’s secret: trace amounts of molecules called macrocyclic lactones, which are produced by soil microorganisms and apparently interrupt the growth of adult barnacle populations.
Barnacle Biology 101
The coating comes from researchers in the Department of Cell and Molecular Biology at the University of Gothenburg, who have studied the biology of barnacles in detail and identified a particularly sensitive stage in the barnacle life cycle.
|Barnacles thrive on a strip of regular hull coating immersed for four months off the coast of Sweden. The rest of the hull had been painted with a copper-free antifouling that contained trace amounts of the macrocyclic lactone called Ivermectin.|
The coating allows the barnacles to colonize in the normal way. But as soon as the young barnacles mature into adult populations, they are unable to establish a fixed location in which to grow. They thus “lose contact and probably die,” the university reported in a release.
The coatings “were found to be effective in preventing colonization by barnacles” on both test panels and boats “for at least two fouling seasons,” the researchers reported in “Multi-seasonal barnacle (Balanus improvisus) protection achieved by trace amounts of a macrocyclic lactone (ivermectin) included in rosin-based coatings,” recently published in the journal Biofouling.
In one test, researchers said they observed no barnacles on the new coating after 388 days, while the barnacles on the control coating had reached a mean of 60 mm2.
In another, the team improved the coatings’ anti-barnacle performance by dissolving the molecules in a co-solvent mixture of propylene glycol and glycerol formal before adding it to the paint base. The co-solvent mixture did decrease the coating hardness, however, the team reported.
Although the additive affects only barnacles, they are considered one of the most difficult fouling organisms to control, and “the growth of algae and similar organisms can be counteracted relatively simply by other methods," the university said.
‘Can Fully Replace Copper’
Field trials of the coatings, tested on leisure craft, show that “the addition of macrocyclic lactones can fully replace copper in coatings used on such craft, on both the eastern and the western coasts of Sweden, and for several seasons,” the university said.
Not only does the coating use no toxins and only trace amounts of macrocyclic lactones, but the researchers say they have also invented new binding agents that shut down the release of the macrocyclic lactones into the marine environment.
Macrocyclic lactones are currently used in low doses as potent antiparasitic medications. The researchers used a common type called ivermectin.
Scientists at the same institution have also been looking into using medetomidine, a veterinary medicine, for keeping larval barnacles from settling on hulls in the first place.